Heat treating apparatus



Aug. 13, 1946. A BANDUR 2 211 311 HEAT TREATING APPARATUS I OriginalFiled Feb. 25, 3.939

Patented Aug. 13, 1940 HEAT TREATING APPARAT S Adolph F. Bandur, Berwyn,Ill., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Original application filed February 25,1938, Serial No. 192,485. Divided and this application filed February18, 1939, Serial No.' 257,177

3 Claims.

This invention relates to heat treating apparatus and more particularlyto apparatus for the heat treatment of finely divided magnetic ma terialsuitable for use in insulated dust cores, and is a division of mycopending application Serial No. 192,485,'fi1ed February 25, 1938. v

In the manufacture of insulated-dust magnetic cores the magnetic metalor alloy is usually cast in an ingot and pulverized to the requiredfineness on suitable apparatus, after which the particles are coatedwith insulation and compressed into required shape. Because thepulverizing action produces internal stresses in the particles whichdetract from their magnetic properties, the particles are annealedbefore they are incorporated in a core. It has been customary to annealthe dust in a conventional sealed pot and, as the dust tends to sinterduring this operation,

' it has generally been necessary to regrind the annealed materialbefore use which results in the restoration of objectional stressestherein.

An object of this invention is the provision of improved heat treatingapparatus for producing finely divided magnetic material possessingmagnetic, electrical and physical properties which are highly desirablein electrical signalling equipment, especially in cores for loadingcoils in telephone circuits.

In one embodiment of the invention comminuted magnetic material in aplurality of shallow trays supported at spaced intervals in a ventilatedcontainer is subjected to a heat treating cycle in a furnace. A cover onthe container has a vent in its central portion through which gasesgener- 35 ated by the magnetic material during one portion of the cycleescape from the container and through which outside air is admitted tothe container during another portion of 'the cycle.

The incoming air passes over a sheet of hot 40 iron which removesoxygenfrom the air. With this procedure and apparatus the dust is effectivelyannealed without sintering, which precludes regrinding, and the treateddust is more adaptable to subsequently applied insulation than 45previous materials, which enables the production of cores having higherpermeability values.

This apparatus is especially suitable for treating nickel-iron magneticalloys of the permalloy type. For convenience the invention will bedescribed in detail as applied to that material, in conjunction with theappended drawing, in which Fig. 1 is an elevation in section of anapparatus for the heat treatment of magnetic dust embodying certainfeatures of the invention, and

(Cl. 263-49) I Fig. 2 is a sectional view of Fig. 1 taken on the line2--2'.

A measured quantity of the magnetic material in the form of finelydivided particles or dust I0 is placed in a shallow fiat-bottomed tray II 5 or pan having sides extending at an angle of about 45 to the planeof the bottom. Inside the tray and welded or otherwise secured to thebottom thereof .are four V-shaped supports it, a conveniently formedfrom strip steel. Each sup- 1o portis mounted-in the tray with the'twolegs of the V extending along the bottom of the tray and the flat topsurfaces of the legs are positioned about below the .top rim of the trayin a plane parallel to the tray bottom. The tray can 15 be made of sheetmetal and a low carbon steel gives good results.

The dust is spread evenly in the tray to a depth governed by thesintering tendency of the particular material under treatment. Sinteringis a function of temperature and pressure, which vary with thecomposition and particle size of the dust, and in each case the depth ofthe dust in the tray is restricted to avoid a fusing pressure on thebottom strata of dust in the tray at the applied temperature. Forpermalloy dust of 120 mesh size a depth of about oneinch is satisfactoryand the optimum value for other materialsis readily determinedexperimentally.

A number of the loaded trays are placed in a so thick walled container13 or box of rectangular shape. The number of trays in each container isbased on handling convenience, but it is advantageous to treat asubstantial quantity of dust in a single container to provide materialof uniform quality. The lower tray rests on the fiat container floor andthe upper trays are successively positioned on the four supports in theadjacently lower tray. On the Supports in the top tray is placed arectangular sheet of iron 4o l4 which extends over the entiresurface ofthe dust in the tray and extends closely to the tray edges on all sides.Y

After the trays and sheet iron are positioned in the container, a fiatcover I5 is placed on the container and its edges are sealed theretowith loam [6 or other suitable medium in a continuous channel I l at thetop of the container into which a peripheral flange ill on the coverextends to provide an efiective seal. At the approximate center of andextending through the cover is a vent l9 about one-eighth inch indiameter providing an opening into the container.

The assembled container is placed in a suitable furnace (not shown) andsubjected to a prescribed heat treating routine. For the treatment ofthe certain types of permalloy dust the container is heated to atemperature around 850 C. and maintained at that temperature for aboutone hour. During this period of heat application an internal pressure isbuilt up in the container due to the development of certain gasesgenerated by heating of the dust. These gases escape from the containerthrough the cover vent and burn in a tapering flame at the outside ofthe cover.

After the completion of the heating cycle the container and contents arecooled at a rate not exceeding 10 C. per minute. During this coolingperiod the gases in the container contract in volume, and the currentflow is consequently reversed, causing air to enter the vent into thecontainer from the furnace chamber. It is desirable to prevent oxidationof the hot dust during this interval and this is accomplished byremoving oxygen from the incoming air by means of the heated iron sheetover the top tray, and the heated trays. Before reaching the dustparticles in the pans the air passes through a labyrinth of hot ironformed by the sheet and trays. The hot iron has a high affinity foroxygen which causes deoxidation of the air and prevents oxidation of thedust. To maintain the full deoxidizing eifectiveness of the labyrinththe trays are cleaned at suitable intervals to remove any surface oxideand the iron sheet is cleaned or replaced periodically.

At the termination of the cooling cycle the dust is removed from thetrays and the particles are coated with suitable insulation such as themixture of magnesium silicate, sodium silicate and magnesium hydroxidedisclosed in applicants Patent 2,105,070 after which the insulatedparticles are compressed at high pressure into the form of a core.

Magnetic particles treated in the described apparatus exhibit new andimproved properties that are valuable in insulated dust cores. Formerly,when the dust was heat treated in a sealed pot any gases generated byheating were largely reabsorbed during the cooling period. Byeliminating these gases and cooling the dust in deoxidized air asprovided in the present disclosure a dust is produced that requires lessinsulation when incorporated in a core. Apparently the describedtreatment imparts to the particles 2. new capacity to receive and retaina thin coating of insulation. Certain types of cores made with permalloyparticles treated in this apparatus required 10% less insulation thandust treated by old methods for equivalent core service. Because of thesmaller percentage of insulation present, the new cores have higherpermeability values than the old structures which enhances the utilityof the cores when they are used in loading coils and similar apparatus.v

The described apparatus can be used for heat treating various types ofmagnetic material and modifications of the apparatus specificallydisclosed herein can be readily adapted to a variety f materials tosupply new and useful properties thereto. It is, therefore, to beunderstood that the invention is restricted only by the scope of theappended claims.

What is claimed is:

1. Apparatus for heat treating finely divided magnetic particles toimprove the magnetic properties of the particles comprising a container,a plurality of individual trays superimposed at definitely spacedintervals in the container and each containing approximately the samequantity oi magnetic particles to be heat treated, a cover sealed to thecontainer and having a vent aligned with the central portion of thesuperimposed trays, and a sheet of iron in the container above the toptray, said sheet being spaced from the vent and from the particles inthe top tray and extending over the surface of the particles in the toptray.

2. In an apparatus for heat treating finely divided magnetic metal forthe purpose of improving the magnetic property of the metal, a containerof substantially rectangular shape, a plurality of superimposed trays inthe container for supporting the finely divided metal, each traycomprising a fiat bottom, side walls extending at an inclined angle tothe bottom, and a plurality of supports secured to the tray bottom forpositioning the adjacent upper tray, a cover for the container having avent in its central portion, and a metal sheet on the supports in thetop tray, the container, trays, metal sheet, and supports beingdimensioned to provide a labyrinth for the passage of air flowing fromthe cover vent to the finely divided metal in the trays.

3. In an apparatus for heat treating finely divided magnetic metal forthe purpose of improving the magnetic properties of the metal, acontainer of substantially rectangular shape, a plurality ofsuperimposed sheet metal trays in the container for supporting thefinely divided metal,

each tray comprising a fiat bottom, side walls extending at an angle ofabout 45 to the bottom, and a plurality of members secured to andprojecting above the tray bottom with their top surfaces in a planeslightly below the top edge of the tray side walls for supporting theadjacent upper tray, a cover for the container having a vent in itscentral portion, and a metal sheet supported on the members in the toptray and extending over the finely divided metal in the tray, thecontainer, trays, metal sheet, and members being dimensioned to form apassage for conducting air from the cover vent to the finely dividedmetal in each of the trays.

ADOLPH F. BANDUR.

